The evolutionary ecology of geographic ranges in western North American Mimulus

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Understanding of the ecological and evolutionary controls over species' ranges lags behind the need to forecast future ranges in an era of rapid environmental change. Major questions include a) when and where geographic range edges are concordant with limits to the ecological niche, b) why niche evolution might fail at range margins, c) how range-limiting processes differ for widespread and endemic species, and d) how ranges will move in response to climate change. A lack of answers hinders management decisions concerning rare species and peripheral populations. This is of particular relevance in Canada, where many species at risk reach their northern limits. The overall goal of this research program is to develop a synthetic understanding of the ecology, evolution and conservation of species' geographic ranges. Near-term research objectives and plans are as follows: (1) Quantify the relative importance of limiting ecological factors across different range edges and for species with contrasting range sizes. We will conduct environmental manipulations and seed introductions to assess the strength of abiotic, biotic, and dispersal limitations. We will also compare physiological niche breadth of widespread and narrowly endemic species. (2) Examine constraints on niche evolution at range margins and for species with contrasting range sizes. We will conduct artificial selection to determine if edge populations lack genetic variation for range expansion. To test the hypothesis that swamping gene flow causes maladaptation at the range edge, we will simulate varying degrees of gene flow from the range interior. We will also examine patterns of niche evolution across the ranges of widespread and rare species. (3) Test methods for refining forecasts of range shifts driven by climate change. We will use experimental results from the above to help parameterize distribution models that evaluate the effects of dispersal limitation, physiological plasticity, biotic interactions, and evolutionary change on potential range shifts. Highly qualified personnel to be trained through this research include four PhD, two MS, and several undergraduate students.